Cold transport line

ABSTRACT

A flexible cold transport line comprises cold transport medium tubes made of a synthetic material which are suspended, by way of flexible wires, from an enveloping radiation shield which is in thermal contact with two cooling medium tubes situated outside the radiation shield; other flexible wires suspend these cooling medium tubes together with the radiation shield inside a flexible bellows which serves as a vacuum jacket.

Sept. 9, 1975 United States Patent [1 1 Prast et a1.

XC C5 5/ n m maa KK 00 3 7777 9999 1111 5972 25 8780 ,9 2950 2900 5 ,5 3333 174/15 C Aupoix et a1. 174/15 C [73] Assignee: U.S. Philips Corporation, New Primary Examiner william F. O,Dea

York, NY.

Assistant Examiner-Ronald C. Capossela Attorney, Agent, or F irmFrank R. Trifari [22] Filed: Oct. 9, 1973 [21] Appl. No.: 404,360

ABSTRACT [30] Foreign Application Priority Data 1972 7214296 A flexible cold transport line comprises cold transport medium tubes made of a synthetic material which are suspended, by way of flexible wires, from an enveloping radiation shield which is in thermal contact with two cooling medium tubes situated outside the radiation shield; other flexible wires suspend these cooling medium tubes together with the radiation shield inside a flexible bellows which serves as a vacuum jacket.

[56] References Cited UNITED STATES PATENTS 10 Claims, 3 Drawing Figures 3,431,347 3/1969 Kafka ct 174/15 C COLD TRANSPORT LINE BACKGROUND OF THE INVENTION The invention relates to a cold transport line, comprising two adjacently extending cold transport medium tubes, a radiation shield which envelops both cold transport medium tubes and which is maintained at a distance therefrom, two cooling medium tubes which extend adjacent to the radiation shield and which are situated on the outside of the radiation shield and are in thermal contact therewith, and a vacuum jacket which envelops the radiation shield and the two cooling medium tubes and which is maintained at a distance therefrom.

A cold transport line of the kind which is the subject of the present invention is known as appears from FIG. 2 of U.S. Pat. No. 3,364,687. In the known cold transport line high-pressure helium flows through the cold transport medium tubes which exchanges heat on the one side with a liquid helium bath and on the other side with an object to be cooled, while liquid nitrogen is transported through the cooling medium tubes for cooling the radiation shield around the cold transport medium tubes of lower temperature.

Instead of using a liquid helium bath as the cold source, use can alternatively be made of a one-stage or multi-stage cold-gas refrigerating machine as described in U.S. Pat. No. 3,473,341, in which helium under pressure can also flow through the cooling medium tubes.

In known cold transport lines of the relevant kind, the cold transport medium tubes, the radiation shield, the cooling medium tubes and the vacuum jacket are rigid components which are held at a distance from each other by spacers. Cold transport lines of this kind are usually made of metal pipes, usually steel or copper. Because of its low expansion coefficient. Invar is sometimes also used for the cold transport medium tubes.

These rigid cold transport lines have various drawbacks. Even though they can be manufactured reasonably well on site for given laboratory set-ups if the overall set-up is known, they are less suitable for factory production. Factory manufacture of rigid cold transport lines which in practice often have a length of 5 to metres, must be effected in parts in view of transport. Assembly of the parts is a time-consuming, complex and expensive and hence undesirable procedure.

The rigid cold transport lines are difficult to handle in practice and their freedom of movement is very limited. Moreover, vibrations originating from the cold source (for example, a refrigerator) and shocks are very liable to be transferred, via the rigid cold transport line, to the object to be cooled (for example, a measuring instrument such as an infrared cell), thus exerting a disturbing effect.

In the cryogenic technique cold transport lines of a different kind are known which serve for simple amplifications and which are hence of a simpler design, comprising an inner tube and an outer tube consisting of flexible bellows (US. Pat. No. 3,240,234).

The use of flexible bellows for the assembly of the two cold transport medium tubes, the radiation shield, the two cooling medium tubes and the vacuum jacket of the subject cold transport line of substantial length, however, would give rise to major structural complications, large diametrical dimensions and high cold losses. High medium pressures in the cold transport medium bellows and cooling medium bellows inside the vacuum jacket would necessitate additional structural provisions in view of the expansion of these bellows as a result of the large pressure differences prevailing thereacross.

The invention has for its object to provide a cold transport line of the kind set forth which, while maintaining simplicity of construction, is completely flexible. Consequently, this transport line can be manufactured in large lengths in factory production, offers a very large freedom of arrangement in cryogenic applications, has small diametrical dimensions and a comparatively light weight, has minimum cold losses and is capable of resisting high medium pressures in the cold transport medium tubes and cooling medium tubes without additional provisions being required.

SUMMARY OF THE INVENTION The cold transport line according to the invention is characterized in that the cold transport medium tubes, the radiation shield and the cooling medium tubes within the vacuum jacket which is constructed as a flexible bellows, are made of a synthetic material. The cold transport medium tubes is locally suspended from the radiation shield by way of flexible wires or bands of a material of low heat conductivity; the radiation shield with the cooling medium tubes is suspended, by way of flexible wires or bands of a material of low heat conductivity, from support ringswhich are locally arranged to be coaxial inside the flexible bellows and which have an outer diameter which is at least substantially equal to the inner diameter of the bellows. Inherent characteristics of such bellows include the variable axial length dimension and flexibility in bending along the axis.

Even though it is often stated in literature that synthetic materials are generally rather brittle at low temperatures, it was found, surprisingly, that cold transport lines of good quality can be used. In a preferred embodiment of the cold transport line according to the invention, the cold transport medium tubes, the cooling medium tubes and the flexible wires or bands are made of nylon. Nylon having a high mechanical strength is thus capable of resisting high pressure forces exerted by high-pressure medium in the cold transport medium tubes and cooling medium tubes. Also nylon can readily take up the tensile forces exerted on the nylon wires or bands as a result of the suspension.

A further preferred embodiment of the cold transport line according to the invention is characterized in that the radiation shield is made of polytetrafluoroethene. Polytetrafluoroethene offers the advantage that it has a high mechanical strength and discharges little gas, with the result that during the cooling3of the cold transport line, during which the vacuum jacket is evacuated, the radiation screen does not release gaseous impurities which disturb the vacuum and which stimulate heat leak-in by radiation.

In a further preferred embodiment the radiation shield is made of polyethylene, which has a high mechanical strength and also discharges little gas. The radiation shield of synthetic material having a comparatively low heat conductivity is cooled by the two cooling medium tubes of synthetic material.

In order to ensure proper heat exchange between the cooling medium tubes and the radiation shield, the radiation shield according to the invention contacts each of the two cooling medium tubes by way of at least one connection of a properly heat-conductive material. This can be effected, for example, by connecting the two cooling medium tubes to the radiation shield by means of a properly heat-conductive contact paste (for example, a paste containing aluminium powder) and/or by wrapping the tubes and the radiation shield with metal tape (for example, copper foil or aluminium foil).

The wrapping with metal tape is attractive in view of its simplicity. However, when put into operation the nylon cooling medium tubes shrink more than the metal tape due to the cooling of the cold transport line. The risk is high that the nylon tubes then become loose with respect to the metal foil envelope, so that proper thermal contact is no longer ensured.

In order to eliminate this drawback, according to the invention a metal tape is wrapped about the assembly of radiation shield and an engaging cooling medium tube, the cooling medium tube which is situated outside the tape envelope exerting a pressure force on the tape envelope at the area of a change-over from the radiation shield to the engaging cooling medium tube. The pressure force can be obtained by means of the nylon suspension wires which are locally wound about the assembly of radiation shield and the two cooling medium tubes. It is thus achieved that, regardless of the comparatively large shrinkage of the nylon cooling medium tubes, the metal tape envelope always remains tensioned and in proper thermal contact with the two cooling medium tubes.

According to another preferred embodiment of the cold transport line according to the invention, a ribbon of a radiation-reflective material is wrapped about the assembly of the metal tape envelope and the cooling medium tube which is situated outside this envelope, for example, a ribbon of a synthetic material which is aluminized on the surface which faces the flexible bellows or on both surfaces. This reduces cold losses caused by radiation.

According to the invention, it is advantageous to provide a protective layer between the metal tape envelope and the radiation-reflective ribbon material. The metal tape, for example, of copper foil or aluminium foil, can readily damage the radiation-reflective ribbon by cutting with its sharp edges. The protective layer ensures that the radiation-reflective ribbon is approxi mately protected. The material of the protective layer should preferably not harden at the low operating temperature. Favourable materials in this respect are, for example, medical gauze and nylon foil.

In another preferred embodiment of the cold transport line according to the invention, a band of radiation-reflective material is wound about the cold transport medium tubes, this band being made, for example, of a synthetic material, its surface facing the radiation shield or both its surfaces being aluminized. This means a further reduction of cold losses caused by radiation.

Another preferred embodiment of the cold transport line according to the invention is characterized in that at an end of the line each of the cold transport medium tube ends and cooling medium tube ends is slid over a connection tube having rigid walls and is clamped thereon by means of two conical sleeves which are slid one into the other. The inner conical sleeve is cut open in its longitudinal direction, the connection tubes being BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of an embodiment of the cold transport line according to the invention.

FIG. 2a is a fragmentary longitudinal sectional view of the coupling of a flexible tube of synthetic material to a connection tube having rigid walls.

FIG. 2b is a cross-sectional view at the area of the line IIbIIb of FIG. 2a.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The reference numeral 1 in FIG. 1 denotes a cold transport line including two cold transport medium tubes 2 enveloped at a distance by a radiation shield 3 of polytetrafluoroethane. Arranged on the outer side of radiation shield 3 are two nylon cooling medium tubes 4 which are in thermal contact with radiation shield 3. Radiation shield 3 and the two cooling medium tubes 4 are enveloped at a distance by stainless steel flexible bellows 5 as a vacuum jacket, while means that the space inside the flexible bellows 5 can be vacuum pumped.

The nylon cold transport medium tubes 2 are locally suspended from the radiation shield 3 by means of nylon wires 6 which are wrapped about these tubes over a part of their length. The suspension is such that the central position of the two cold transport medium tubes 2 with respect to the radiation shield 3 is maintained.

The radiation shield 3 is suspended, together with the cooling medium tubes 4, by way of nylon bands 7 from aluminium support rings 8, a number of which are ar-. 'ranged, distributed over the length of the cold transport line 1, to be coaxial within flexible bellows 5. The outer diameter of support ring 8 is substantially equal to the inner diameter of flexible bellows 5. Consequently, the support ring has a tight fit inside the bellows and no further fixing means are required.

One of the two cooling medium tubes 4 permanently engages the radiation shield 3, via a contact layer 9 of heatconductive material, i.e., a paste containing aluminium powder. A tape 10 of copper foil is wrapped around the assembly of said cooling medium tube and radiation shield. The other cooling medium tube is arranged at one of the two locations where the tape envelope changes over from the radiation shield to the permanently engaging cooling medium tube and presses against the tape envelope at thisarea.

The heat-conductive layer 9 and the copper foil tape ensure proper thermal contact between the cooling medium tubes 4 and the radiation shield 3 to be cooled.

During cooling from room temperature to the low operating temperature, the nylon cooling medium tubes 4 shrink more than copper foil 10. The proper thermal contact between the cooling medium tubes and the radiation shield, however, is maintained. The cooling medium tube which is situated outside the envelope of copper foil tape then presses the envelope inwards, with the result that the latter continues to engage both the radiation shield 3 and the cooling medium tube inside the envelope.

In order to reduce cold losses due to radiation, a radiation-reflective ribbon 11, consisting of a foil of the synthetic material known as Mylar having an aluminium outer surface, is wrapped around the assembly of the copper foil tape envelope l0 and the cooling medium tube 4 which is situated outside this envelope.

Present between the aluminized Mylar ribbon 11 and the copper foil 10 is a layer of gauze 12 which prevents the Mylar from being damaged by the sharp edges of the copper foil. Cold losses due to radiation can be further reduced by wrapping also the two cold transport medium tubes 2 with a radiation-reflective band 13 of aluminized Mylar.

The described cold transport line has been constructed and tested with favorable results. The length of the line was 10 metres and the outer diameter 75 mm. The nylon cold transport medium tubes had an inner diameter of 5 mm and an outer diameter of 7 mm. The outer diameter of the polytetrafluoroethene radiation shield was 28 mm and its wall thickness 2 mm. The outer diameter of the cooling medium tubes was 8 mm; the wall thickness also was 2 mm. The two cold transport medium tubes were suspended from the radiation shield every cm, while the distance between the aluminium rings from which the assembly of radiation shield and cooling medium tubes was suspended was 40 FIG. 2 shows how an end 20 of one of the four nylon tubes (cold transport medium tubes and cooling medium tubes) is coupled to a steel connection tube 21. Accordingly, the end 20 is slid over connection tube 21 and is clamped thereon by conical sleeves 22 and 23 which are inserted one into the other. The inner sleeve 22 is longitudinally cut open so as to obtain an improved clamping action. Like the three other tubes not shown, connection tube 21 is passed out through rigid end wall 24 of flexible bellows 5.

Even though the drawing shows only one embodiment of the cold transport line according to the invention, it will be obvious that a variety of other embodiments are feasible within the scope of the invention.

What is claimed is:

l. A cold transport line comprising first tube means for cold transport medium, a radiation shield surrounding said first tube means with a first annular space defined between said shield and first tube means, first flexible wire means of low heat-conductivity engaging and suspending said first tube means within said shield, second tube means for cooling medium situated outside and parallel to said shield and in thermal contact therewith, a vacuum jacket formed as a flexible tubular bellows surrounding said shield with a second annular space defined between said jacket and shield, second flexible wire means of low heat-conductivity engaging and suspending said shield within said jacket, said first and second tube means, radiation shield and jacket made of synthetic material, and sealing means closing the ends of said jacket about said first and second tube means and shield for defining said vacuum space therein.

2. Apparatus according to claim 1 further comprising a plurality of axially spaced-apart rings fixedly positioned generally concentrically within said bellows, said second flexible wire means engaging said rings and said shield.

3. Apparatus according to claim 1 wherein said sealing means comprises a wall closing each end of said bellows, each wall including apertures corresponding to said first and second tube means, and a connection tube secured in each aperture with one end of the connection tube engaging one end of one of said tube means.

4. Apparatus according to claim 1 wherein said first and second tube means and first and second wire means are made of nylon.

5. Apparatus according to claim 1 wherein said radiation shield is made of polytetrafluoroethene.

6. Apparatus according to claim 1 wherein said radiation shield is made of polyethylene.

7. Apparatus according to claim 1 wherein said second tube means comprises first and second tubes, the first tube being in thermal contact with said shield, and heat conducting tape wrapped around and enveloping said first tube and shield with a portion of said tape extending between said first tube and said shield, said second tube situated parallel to said first tube, outside said tape, and means urging said second tube inwardly against said portion of tape, and thereby maintaining this tape in tension despite shrinkage of the tubes during transport of cold medium therethrough.

8. Apparatus according to claim 7 wherein said tape comprises copper foil.

9. Apparatus according to claim 7 further comprising a layer of radiation reflective ribbon wrapped around and enveloping said first and second tubes and tape.

10. A cold transport line comprising first tube means for cold transport medium, a radiation shield surrounding said first tube means with a first annular space defined between said shield and first tube means, first flexible wire means of low heat-conductivity engaging and suspending said first tube means within said shield, second tube means comprising first and second tubes for cooling medium situated outside and parallel to said shield, with the first tube in thermal contact with said shield and heat conducting tape wrapped around and enveloping said first tube and shield with a portion of said tape extending between said first tube and said shield, said second tube situated parallel to said first tube and outside said tape, and means urging said second tube inwardly against said portion of tape and thereby maintaining this tape in tension despite shrinkage of the tubes during transport of cold medium there through, a tubular vacuum jacket surrounding said shield with a second annular space defined between said jacket and shield, second flexible wire means of low heat-conductivity engaging and suspending said shield within said jacket, said first and second tube means, radiation shield and jacket made of synthetic material, and sealing means closing the ends of said jacket about said first and second tube means and shield for defining said vacuum space therein. 

1. A COLD TRANSPORT LINE COMPRISING FIRST TUBE MEANS FOR COLD TRANSPORT MEDIUM, A RADIATION SHIELD SURROUNDING SAID FIRST TUBE MEANS WITH A FIRST ANNULAR SPACE DEFINED BETWEEN SAID SHIELD AND FIRST TUBE MEANS, FIRST FLEXIBLE WIRE MEANS OF LOW HEAT-CONDUCTIVITY ENGAGING AND SUSPENDING SAID FIRST TUBE MEANS WITHIN SAID SHIELD, SECOND TUBE MEANS FOR COOLING MEDIUM SITUATED OUTSIDE AND PARALLEL TO SAID SHIELD AND IN THERMAL CONTACT THEREWITH, A VACUUM JACKET FORMED AS A FLEXIBLE TUBULAR BELLOWS SURROUNDING SAID SHIELD WITH A SECOND ANNULAR SPACED DEFINED BETWEEN SAID JACKET AND SHIELD, SECOND FLEXIBLE WIRE MEANS OF LOW HEAT-CONDUCTIVITY ENGAGING AND SUSPENDING SAID SHIELD WITHIN SAID JACKET, SAID FIRST AND SECOND TUBE MEANS, RADIATION SHIELD AND JACKET MADE OF SYNTHETIC MATERIAL, AND SEALING MEANS CLOSING THE ENDS OF SAID JACKET ABOUT SAID FIRST AND SECOND TUBE MEANS AND SHIELD FOR DEFINING SAID VACUUM SPACE THEREIN.
 2. Apparatus according to claim 1 further comprising a plurality of axially spaced-apart rings fixedly positioned generally concentrically within said bellows, said second flexible wire means engaging said rings and said shield.
 3. Apparatus according to claim 1 wherein said sealing means comprises a wall closing each end of said bellows, each wall including apertures corresponding to said first and second tube means, and a connection tube secured in each aperture with one end of the connection tube engaging one end of one of said tube means.
 4. Apparatus according to claim 1 wherein said first and second tube means and first and second wire means are made of nylon.
 5. Apparatus according to claim 1 wherein said radiation shield is made of polytetrafluoroethene.
 6. Apparatus according to claim 1 wherein said radiation shield is made of polyethylene.
 7. Apparatus according to claim 1 wherein said second tube means comprises first and second tubes, the first tube being in thermal contact with said shield, and heat conducting tape wrapped around and enveloping said first tube and shield with a portion of said tape extending between said first tube and said shield, said second tube situated parallel to said first tube, outside said tape, and means urging said second tube inwardly against said portion of tape, and thereby maintaining this tape in tension despite shrinkage of the tubes during transport of cold medium therethrough.
 8. Apparatus according to claim 7 wherein said tape comprises copper foil.
 9. Apparatus according to claim 7 further comprising a layer of radiation reflective ribbon wrapped around and enveloping said first and second tubes and tape.
 10. A cold transport line comprising first tube means for cold transport medium, a radiation shield surrounding said first tube means with a first annular space defined between said shield and first tube means, first flexible wire means of low heat-conductivity engaging and suspending said first tube means within said shield, second tube means comprising first and second tubes for cooling medium situated outside and parallel to said shield, with the first tube in thermal contact with said shield and heat conducting tape wrapped around and enveloping said first tube and shield with a portion of said tape extending between said first tube and said shield, said second tube situated parallel to said first tube and outside said tape, and means urging said second tube inwardly against said portion of tape and thereby maintaining this tape in tension despite shrinkage of the tubes during transport of cold medium therethrough, a tubular vacuum jacket surrounding said shield with a second annular space defined between said jacket and shield, second flexible wire means of low heat-conductivity engaging and suspending said shield within said jacket, said first and second tube means, radiation shield and jacket made of synthetic material, and sealing means closing the ends of said jacket about said first and second tube means and shield for defining said vacuum space therein. 